Nonreciprocal microstrip ferrite phase shifter having regions of circular polarization



Dec. 24, 1968 H ET AL 3,418,605

NONRECIPROCAL MI-CROSTRIP FERRITE PHASE SHIFTER HAVING REGIONS OF CIRCULAR POLARIZATION Filed June 30. 1966 2 Sheets-Sheet 1 FIG; 1

FIG 3 LATCHING FERRITE 5% :1;- .P..i 1ac3 TCZ INVENTORS Hu h A. Half Gerar T. Roome Carl W. Gersi Edgar E.Des-Jard| ns Edward J. Domlck BY%&L 7%M ATTO NEYS Dec. 24, 1968 HA|R ETAL 3,418,605

NONRECIPROCAL MICROSTRIP FERRITE PHASE SHIFTER HAVING REGIONS 0F CIRCULAR POLARIZATION Filed June 30, 1966 2 Sheets-Sheet 3 United States Patent NONRECIPROCAL MICROSTRIP FERRITE PHASE SHIFTER HAVING REGIONS OF CIRCULAR POLARIZATION Hugh A. Hair, Liverpool, Gerald T. Roome, Syracuse,

Carl W. Gerst, North Syracuse, and Edgar E. Des- Jardins and Edward J. Domick, Syracuse, N.Y., assignors to Research Corporation, New York, N.Y., a corporation of New York Filed June 30, 1966, Ser. No. 561,792 12 Claims. (Cl. 33324.1)

ABSTRACT OF THE DISCLOSURE A nonreciprocal phase-shifting device comprises at least one planar ground-plane element and a signal conductor which cooperate to form a guide-microwave-energy path. The signal conductor is so contoured, such as having a meandering path, to establish a circularly polarized radio frequency-magnetic field component in a given region such as between the ground-plane element and the signal conductor. A planar self-latching ferrite is in the given region. Magnetization-switching means selectively switch the remanent magnetization in the ferrite element.

This invention pertains to nonreciprocal microwave devices and more particularly to nonreciprocal phaseshifting devices for microwave systems.

A nonreciprocal phase-shifting device is one which will shift by a given amount the phase of the microwave energy passing, in one direction, through the device and will shift by a different amount or not at all, the phase of the microwave energy passing, in the opposite direction through the device. Such phase-shifting devices are used in components of microwave systems such as switches, hybrid junctions and circulators.

Presently available nonreciprocal phase-shifting devices are complicated and bulky. In the past few years there has been a trend to the miniaturization of components and integrated circuitry. Such a trend is ideally suited for the upper end of the microwave energy spectrum. Presently available phase-shifting devices using bulk-ferrite elements are impractical in such environments. It is both difficult and expensive to devise a hybrid system including both microelectric devices and integrated circuits having planar geometry and bulk-material devices having volumetric geometry. In fact, such systems may be impossible to assemble when microwaves in the millimeter range are to be processed.

It is accordingly a general object of the invention to provide improved nonreciprocal phase-shifting devices for microwave systems which are extremely small and light in weight,

It is another object of the invention to provide improved nonreciprocal phase-shifting devices which are relatively inexpensive to mass produce by exploiting presently known printed and integrated circuit techniques.

It is a further object of the invention to provide improved nonreciprocal phase-shifting devices which are completely passive, or which do not require continuously operating external sources of electrical or magnetic energy to control the phase of microwave signals.

Briefly, the nonreciprocal phase-shifting device contemplated by the invention comprises at least one planar ground-plane element and a single signal conductor disposed in a first plane parallel to the plane of the groundplane element. The signal conductor and the ground-plane element are spaced from each other in cooperating relation to provide a guided-microwave-energy path. In its plane the signal conductor is so contoured to establish 3,418,605 Patented Dec. 24, 1968 ice within a given region, external to that plane, a radiofrequency-magnetic field having a component which is circularly polarized. (It should be noted that an elliptically polarized field can be considered to have a circularly polarized component.) The circularly polarized component is directed along a first line in a second plane parallel to the plane of the ground-plane element. A selflatching-ferrite element is disposed to include the given region. Such an element is one which remains in a state of remanent magnetization after the removal of a magnetizing field. Magnetization-switching means are provided for selectively switching the remanent magnetization of the ferrite element between opposite senses at least along the aforesaid first line. Microwave-energy terminal means are at one end of the signal conductor and the ground-plane element, and at the other end of the signal conductor and the ground-plane element respectively. Each of the microwave-energy terminal means can be either an input means or an output means depending on the actual use of the device. For example, the input and output terminals will depend generally on the direction of microwave-energy flow through the device.

A feature of the invention concerns the actual configuration of the elements which exploit printed-circuit techniques.

Other objects, features and advantages of the invention will be apparent from the following detailed description when read with the accompanying drawings which show, by way of example and not limitation, apparatus for practicing the invention.

In the drawings:

FIGURE 1 is an enlarged top plane view of a portion of a non-reciprocal phase-shifting device showing a signal conductor disposed on a self-latching-ferrite element;

FIGURE 2 is a sectional view, taken along the line 2--2 of FIG. 1, showing the preferred disposition of the signal conductor, the ferrite element and the ground-plane element, as well as the interacting fields required to explain the operation of the invention;

FIGURE 3 is a perspective view of an entire nonreciprocal phase-shifting device including magnetizationswitching means in accordance with one embodiment of the invention.

FIGURE 4 is a perspective view of another nonreciprocal phase-shifting device including a different magnetizationswitching means in accordance with another embodiment of the invention; and

FIGURES 5 and 6 are quasi-schematic representations of the nonreciprocal phase-shifting devices showing means for increasing the interaction between the remanent magnetization of the ferrite element and the fields generated by the signal conductor and the ground-planeelernent.

In a guided-microwave-energy path the velocity of the flow of the microwave energy is a function of at least the permeability of the medium of the path. Therefore, changes in the medium permeability introduce changes in the velocity of energy flow. These changes in velocity can be equated to changes in the electrical length of the path. A change in the electrical path length is equivalent to a differential delay or phase-shift in the microwave signal propagated along the path. Hence, by knowing the available change of permeability in the path and then choosing a mechanical length for the path, any desired differential phase-shift can be obtained. It should be noted that any mechanical path will introduce a delay or phase-shift in the microwave energy solely by virtue of its mechanical length. The change in permeability in the path superimposes on this phase-shift a further phase-shift (a differential phase-shift). Throughout the text the phrase phase-shift means the differential phase-shift.

Changes in the permeability in the path are obtained by introducing a ferrite material in the path and then controlling the direction of magnetization of the ferrite material with respect to the direction of polarization of the RF (radio frequency)-magnetic field component of the microwave energy flowing down the path.

For example, assume a microwave signal is transmitted along a guided-microwave-energy path with a circularly polarized, RF-magnetic field component wherein the axis and sense of rotation of that field is represented by a vector in a given direction. If a magnetized ferrite element is included in the path there can be an interaction between the domains of the ferrite element and the magnetic field of the microwave signal. In particular, when the magnetization vector, representing predominant alignment of the domains in a region of the ferrite element has the same direction as the vector representing the axis and sense of rotation of the circularly polarized RF- magnetic field in that region, there is an interaction between the so aligned domains and the magnetic field, and the permeability of that region changes. If the vectors are oppositely directed there is little interaction and the permeability remains relatively unchanged. Furthermore, orthogonality of the vectors results in little interaction. This condition represents the outer limits of the change in permeability. In those cases where the vectors are not colinear the magnetization vector can be resolved into a colinear and a transverse component with only the colinear component being involved in the interaction. The scope of the invention contemplates such a condition.

To summarize, in order to obtain a nonreciprocal phase-shift there must be a nonreciprocal interaction between the RF-magnetic field of the microwave energy flowing down a guided-microwave-energy path and ferrite medium in the path to affect the permeability of the path. The nonreciprocal interaction can be obtained by generating a circularly polarized RF-magnetic field in a suitably magnetized ferrite medium. Such a condition can be produced by the circuit shown in FIGURES 1 and 2. In particular, the circuit is shown comprising a planar ground-plane element 12 and a signal conductor 14 having convolution elements 14A, 14B, 14C and 14D. Ground-plane element 12 and signal conductor 14 are spaced from each other to provide a guided-microwaveenergy path which is known as a microstrip line. It is possible to have another ground-plane element spaced above signal conductor 14 to provide a strip line. When microwave energy is applied to the microstrip line for the left side, current flows through signal conductor 14 as represented by the arrowheaded line 16 of FIG. 1 and the dots 18 and crosses 20 in the convolution elements 14A to 14D FIG. 2). The RF-current through element 148 generates the conventional RF-magnetic field represented by circle 22 and the RF-current through element 14C generates the conventional RF-magnetic field represented by circle 24.

At the points A and A, the RF-magnetic field H arising from current through element 143 is spatially orthogonal to the RIF-magnetic field H arising from current through element 14C. The resultant magnetic field is represented by vector H In order to cause vector H to rotate or to produce a circularly-polarized, RF-magnetic field at point A the fields H and H must be 90 out of (time) phase. This condition is readily accomplished if the length L of each of the convolution elements 14A to 14D is an odd number of operating quarter wavelengths. When this is so, the resultant magnetic field is circularly polarized and vector H can be assumed to rotate in a counter-clockwise manner. Its axis of rotation is perpendicular to the plane of FIG. 2, passing through point A. It can be represented by a vector directed inward to the page of the figure. If current flow were in the opposite direction, the resultant magnetic field would be circularly polarized in a clockwise sense and its rotational vector representation would be directed outward of the page of the figure. Of course, it should be realized that magnetic fields produced by the current flowing in elements 14A and 14B, and elements 14C and 14D similarly interact and produce similarly circularly polarized RF-magnetic field points at B and C, respectively. The fields are not shown, solely for the sake of simplicity.

In other regions, the relative time-phase between the currents falls off (or increases) linearly with distance from the midpoints of the elements and the type of polarization varies from circular at the center through elliptical to linear at the ends of the elements. However, the elliptical polarization has, in a sense, a circular component.

If now a ferrite element is placed in the region of rotational polarization and it is suitably magnetized; the interaction required for nonreciprocal phase-shifting is obtained. Accordingly, the ferrite element 26 is placed in the guided-microwave-energy path and in particular between signal conductor 14 and ground-plane element 12. When ferrite element 26 is magnetized in the same direction as the rotational vector representation of the circularly polarized-magnetic field there will be an interaction between the domains of the ferrite material; if in the opposite direction there will be no interaction. Four cases arise:

(1) Microwave energy is transmitted along the direction indicated by arrowheaded line 16 and the magnetization of the ferrite element is in the direction indicated by arrow 28. There is a phase-shift.

(2) Microwave energy is transmitted along the direction indicated by arrowheaded line 16 and the magnetization of the ferrite element is in the direction indicated by arrow 30. There is no phase-shift.

(3) Microwave energy is transmitted along a direction opposite to that indicated by line 16 and the magnetization of the ferrite element is in the direction indicated by arrow 28. There is no phase-shift. (4) Microwave energy is transmitted along a direction opposite to that indicated by line 16 and the magnetization of the ferrite element is in the direction indicated by arrow 30. There is a phase-shift.

Practical realizations of the device will now be described.

In FIGURE 3, there is shown a nonreciprocal phaseshifting device 30 comprising planar ground-plane element 32, a planar self-latching-ferrite element 34 having an aperture 36, a signal conductor 38 and a control conductor (magnetization-switching means) 40.

Signal conductor 38 is spaced from ground-plane element 32 to establish a guided-microwave-energy path which is known as a microstrip line. Microwave energy will propagate down the line in the TEM mode. It is also possible to have another ground-plane element spaced above signal conductor 16 to provide a strip line Such a change is contemplated within the scope of the invention.

Signal conductor 38 has a transmission terminal TSl, a plurality of serially convolution elements 38A to 381 and another transmission terminal TSZ. The convolution elements are in substantially parallel relationship and each is an odd number of operating quarter wavelengths long.

Ferrite element 34 is preferably disposed between ground-plane element 32 and signal conductor 38. However, it should be noted that it is possible to place element 34 above signal conductor 38. It is only necessary that it be in a region of the circularly polarized magnetic field. While signal conductor 38 is shown as a wirelike conductor, it should be noted that it is preferable to print it directly on ferrite element 34. Printing is used in its generic sense to include evaporating, sputtering, photoetching or other techniques well known in the arts of printed circuitry and microelectronic fabrication. Similarly it may be desirable to print ground-plane element 32 on ferrite element 34.

Transmission terminals T61 and TG2 are connected to ground-plane element 32; and terminals TC1 and TCZ are connected to control conductor 40. Microwave signals may be applied to terminals T S1 and TGl and received from terminals T82 and TG2. The state of magnetization (remanent) of ferrite element 34 is determined by the direction of current applied to control conductor 40 via terminals TC1 and TC2.

When an electric-current pulse is applied across terminals TC1 and TC2, a remanent magnetization is established in ferrite element 34. Its pattern will be substantially circular closed curves, concentric with aperture 36, in planes parallel to ground-plane element 32. The magnetization can be resolved into components longitudinal and transverse to the convolution elements. The longitudinal components will be directed from left to right if the magnetization is clockwise resulting from current flow from terminal TC1 to TC2; and they will be directed from right to left if the magnetization is counter-clockwise resulting from current flow from terminal TC2 to terminal TC1. There will or will not be a phase-shift depending on the direction of microwave-energy flow as previously described.

It should be noted that the self-latching ability of the ferrite element is obtained by virtue of the aperture resulting in closed lines on magnetization. However, selflatching can be obtained in an unapertured ferrite element which satisfies the following condition:

H is greater than 41rM (t)/l where:

H =the coercivity of the ferrite material M =the saturation magnetization of the ferrite material t=the thickness of the ferrite element l=the length of the ferrite element.

When such a ferrite element is utilized, further advantages are obtained. In particular, the ferrite element can be a thin film printed on a ground-plate element and the control conductor can also be printed on the ground-plane element.

Such an embodiment is shown as the nonreciprocal phase-shifting device 50 in FIG. 4. Since many of the components are the same, primed reference characters will be used and only the differences will be discussed. The basic difference is that ferrite element 52 is unapartured and magnetization is obtained by transmitting current through control conductor 56 which is oriented orthogonal to convolution elements 38A to 38E. Conductor 56 is preferably printed on the insulated bottom layer 54 of ground-plane element 34'. When a pulse of current is transmitted from terminal TC1 via control conductor 56 to terminal TC2, magnetization is established in the plane of ferrite element 52 from left to right. Current flow in the opposite direction establishes a rightto-left magnetization in ferrite element 52.

In the embodiment of FIGURE 4 the major portion of the magnetization is colinear with the convolution elements whereas in FIGURE 3 a minor portion of the magnetization is so oriented. However, it is possible to modify the apertured ferrite element to increase the interaction.

In FIGURE 5, there is shown a modified ferrite element 34A with an enlarged rectangular aperture 36A. The magnetization is thus constrained to follow more rectangular paths with greater portions of its parallel to the convolution elements of signal conductor 38". The same effect is obtained by using a pair of apertures as shown in FIGURE 6. Ferrite element 34B is provided with a pair of spaced apertures 38C which are threaded in parallel by control conductor 40". The magnetization generated by the current flowing through apertures 36C interact to constrain the resultant magnetization to assume more rectangular paths.

There has thus been shown an improved nonreciprocal phase-shifting device which employs a self-latching-ferrite element disposed in a guided-microwave-energy path and remanently magnetized in directions colinear with the direction of the circularly polarized-magnetic field travelling along the path. By making the ferrite element self-latching there is no need for the continuous application of magnetizing energy. Furthermore, the construction of signal conductor and the ground-plane element make the device assume a planar configuration and so permit its easy fabrication and miniaturization.

In a device made in accordance with the embodiment of FIGURE 3, the ferrite element had a length of 1.0 in., a width of 0.6 in. and a thickness of 0.020 in. The device could be switched in 50 nanoseconds with a power of 1.0 micro-joule. The device introduced a degree differential phase-shift in a microwave signal having an operating frequency of 3.6 gHz. with loss of only 1.5 db. The ferrite employed was TTI-414 having a coercivity of 0.7 0e. and a saturation magnetization of 700 gauss.

While only a limited number of embodiments have been shown and described in detail, there will now be obvious to those skilled in the art many modifications and variations which while satisfying many or all of the objects of the invention do not depart from the spirit thereof, as defined in the appended claims.

What is claimed is:

1. A nonreciprocal phase-shifting device comprising at least one planar ground-plane element, a single signal conductor disposed in a first plane parallel to the plane of said ground-plane element, said signal conductor and said ground-plane element being spaced from each other in cooperating relation to provide a guided-microwaveenergy path, said signal conductor being so contoured to establish within a given region a radio frequency-magnetic field having a component which is circularly polarized, the rotational axis of the circularly polarized component being directed along a first line in a second plane parallel to the plane of said ground-plane element, a self-latching-ferrite element having a planar geometry, said ferrite element being disposed to include said given region and in a plane parallel to the plane of said ground-plane element, magnetization-switching means for selectively switching the remanent magnetization of said ferrite element between opposite senses at least along said first line, and first and second microwaveenergy transmission means disposed at one end of said signal conductor and said ground-plane element, and at the other end of said signal conductor and said groundplane element respectively.

2. The nonreciprocal-phase-shifting device of claim 1 wherein said signal conductor is formed by a plurality of convolution elements, electrically connected in series, which are physically disposed in adjacent, substantially parallel relationship, each of said convolution elements being an odd number of operating quarter wavelengths.

3. The nonreciprocal phase-shifting device of claim 2 wherein at least one pair of adjacent convolution elements are so spaced from each other that the radio frequency fields generated by said convolution elements when receiving microwave energy interact to establish said radio frequency field having a component which is circularly polarized.

4. The nonreciprocal phase-shifting device of claim 3 wherein said ferrite element is provided with at least one aperture, and said magnetization-switching means comprises a control conductor passing through said aperture and adapted to receive electric-current pulses having first or second polarities.

5. The nonreciprocal phase-shifting device of claim 3 wherein said magnetization-switching means comprises a control conductor disposed in a plane parallel to the plane of said ferrite element and directed along a line perpendicular to said convolution elements, and is adapted to receive electric-current pulses having first or second polarities.

6. The nonreciprocal phase-shifting device of claim 3 wherein said ferrite element is disposed between said ground-plane element and said signal conductor.

7. The nonreciprocal phase-shifting device of claim 6 wherein said ferrite element is disposed on said groundplane element and said signal conductor is printed on said ferrite element.

8. The nonreciprocal phase-shifting device of claim 7 wherein said ferrite element is a film of ferrite material printed on said ground-plane element.

9. The nonreciprocal phase-shifting device of claim 7 wherein said ferrite element is provided with at least one aperture, and said magnetization-switching means comprises a control conductor passing through said aperture and adapted to receive electric-current pulses having first or second polarities.

10. The nonreciprocal phase-shifting device of claim 7 wherein said magnetization-switching means comprises a control conductor disposed in a plane parallel to the plane of said ferrite element and directed along a line perpendicular to said convolution elements, and is adapted to receive electric-current pulses having first or second polarities.

11. The nonreciprocal phase-shifting device of claim 10 wherein said control conductor is insulatively disposed on the side of said ground-plane element remote from said ferrite element.

12. The nonreciprocal phase-shifting device of claim 11 wherein said control conductor is printed on said ground-plane element.

References Cited UNITED STATES PATENTS 3,257,629 6/1966 Kornreich 333-31 3,277,401 10/1966 Stern 333-24.1 3,289,110 11/1966 Weiss 333-24.1

HERMAN KARL SAALBACH, Primary Examiner.

PAUL GENSLER, Examiner. 

